The kinetics of the epoxidation of soybean oil and the extent of side reactions were studied at 40, 60 and 80°C. Epoxidation was carried out in toluene with "in situ " formed peroxoacetic and peroxoformic acid and in the presence of an ion exchange resin as the catalyst. The reaction was found to be first-order with respect to the double bond concentration. At higher temperatures and at higher conversions a deviation from the first-order kinetics was observed. The rate constants for the epoxidation with peroxoacetic acid were 0.118 (h -1 ) at 40°C, 0.451 (h -1 ) at 60°C and 1.278 (h -1 ) at 80°C, while those for peroxoformic acid were 0.264, 0.734, and 1.250 (h -1 ). The activation energy was found to be 54.7 kJ/mol for the epoxidation with peroxoacetic acid and 35.9 kJ/mol for that with peroxoformic acid. Three factors indicated that side reactions did not occur on a large scale: The absence of an OH band in the IR spectra, the formation of less than 2% of higher molecular weight products from gel permeation chromatography and the selectivity values between 0.9 and 1.

The kinetics of the epoxidation of soybean oil in bulk by peracetic acid formed in situ, in the presence of an ion exchange resin as the catalyst, was studied. The proposed kinetic model takes into consideration two side reactions of the epoxy ring opening involving the formation of hydroxy acetate and hydroxyl groups as well as the reactions of the formation of the peracid and epoxy groups. The catalytic reaction of the peracetic acid formation was characterized by adsorption of only acetic acid and peracetic acid on the active catalyst sites, and irreversible surface reaction was the overall rate-determining step. Kinetic parameters were estimated by fitting experimental data using the Marquardt method. Good agreement between the calculated and experimental data indicated that the proposed kinetic model was correct. The effect of different reaction variables on epoxidation was also discussed. The conditions for obtaining optimal epoxide yield (91% conversion, 5.99% epoxide content in product) were found to be: 0.5 mole of glacial acetic acid and 1.1 mole of hydrogen peroxide (30% aqueous solution) per mole of ethylenic unsaturation, in the presence of 5 wt% of the ion exchange resin at 75°C, over the reaction period of 8 h.Paper no. J9753 in JAOCS 78, 725-731 (July 2001).Although numerous references exist in the literature concerning the methods of epoxidation of different olefinic substrates, many fewer are concerned with the kinetics of epoxidation. The kinetics of the process depend on the reaction conditions. Epoxidation of vegetable oils can be carried out in solution or in bulk, with in situ (1-3) formed or preformed peracids (4-9), with homogeneous or heterogeneous catalysts. A kinetic model for in situ epoxidation of anchovy oil with partially preformed peracetic acid in the presence of a resin catalyst was reported (10). In the range of the operating variables, epoxidation and ring opening were described by a pseudo first-order reaction, applying the principle of the stationary state. Two studies of the kinetics of the in situ epoxidation of oleic acid with hydrogen peroxide and acetic acid and of methyl esters of palm olein by performic and peracetic acid, both carried out in the presence of sulfuric acid as a catalyst, concluded that the rate-determining step of the epoxidation process was the formation of peracetic (or performic) acid (11,12). Rangarajan et al. (13) reported kinetic parameters for the in situ epoxidation of soybean oil by peracetic acid, again in the presence of sulfuric acid as the catalyst, but treated it as a two-phase system. Significantly higher rates were obtained when heat and mass transfer limitations were removed. The proposed model also predicted the effect of the addition of an inert solvent on epoxidation.With an acidic ion exchange resin as the catalyst for the epoxidation of vegetable oils, the porous structure of the solid catalyst and the size of the natural unsaturated triglycerides were found to minimize side reactions and thus improve selectivity (SE) (14). The p...

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Phytosterols in Cucurbita pepo convar. citrullina seed oil were analyzed by GC-MS after extraction by the organic solvents, hexane and petroleum ether, and by supercritical carbon dioxide at 400 bar and 408C. Desmosterol, campesterol, stigmasterol, spinasterol, D7,22, D7stigmastenol, D7,, and D7-avenasterol were identified mass spectrometrically via detection of the parent molecular ions and fragmentation patterns of corresponding trimethylsilyl derivatives. The used derivatizing agents N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) are equally effective for phytosterol content determination. As expected, the predominant phytosterols were D7-sterols that ranged from 91.0 to 94.2% of the total phytosterol content given as sum of free sterols and steryl esters. Comparison of extraction methods revealed that, although the oil yields obtained by extraction with hexane, petroleum ether and supercritical CO 2 were 43.37, 44.65, and 36.17%, respectively, the total phytosterol content in supercritical CO 2 extract (294 mg/100 g oil, for both MSTFA and BSTFA) was about 30% higher than in hexane and about 20% higher than in petroleum ether extract.Practical applications: Extraction with the application of fluids in supercritical state opens a new approach to the production of edible vegetable oils. Many economical, health, and environmental aspects are interlaced in this modern approach. By applying the supercritical extraction, the selectivity of the extraction can be significantly improved compared to traditional methods of extraction. Thus, depending on the operating conditions of supercritical CO 2 extraction higher total phytosterol content can be achieved resulting in improved nutritional value of the pumpkin seed oil.

Mathematical models that describe the kinetics of reaction systems for the in situ epoxidation of unsaturated fatty acid esters or triglycérides with organic peracids are reviewed in this paper. The advantages and inadequacies of each model are discussed. A mono-phase pseudo-first order kinetic model was compared with a two phase model based on the Langmuir-Hinshelwood-Hougen-Watson (LHHW) postulates proposed by the authors of this paper. The comparison was performed on the experimentally determined values for the in situ epoxidation of soybean oil by peracetic acid in the presence of different quantities of ion exchange resin used as the catalyst. It was concluded that a complete model for in situ epoxidation in the presence of ion exchange resin as the catalyst was still not given for perorganic acid formation. In particular, we report here the possibilities of the creation of an "ideal" model for in situ epoxidation

The kinetics of the epoxidation of castor oil in benzene with peracetic acid formed in situ from acetic acid and hydrogen peroxide in the presence of an ion-exchange resin as a catalyst was studied. Eighteen pseudo-two-phase models are established that, besides the main reactions of peracid and epoxy ring formation, also consider the side reaction of epoxy ring cleavage with acetic acid. Kinetic expressions for the heterogeneously catalyzed peracetic acid formation are developed on the basis of Eley–Rideal and Langmuir–Hinshelwood–Hougen–Watson postulates. An equation derived for the temperature dependency of the chemical equilibrium constant for peracetic acid formation is applied. Kinetic and adsorption parameters were estimated by fitting experimental data using the Marquardt method. The best-fit model correctly interprets data of double bond and epoxy group contents as a function of reactant ratios, catalyst concentrations, and temperatures applied during epoxidation. The proposed model better fits experimental data than the pseudohomogeneous model reported in the literature.

An expression for temperature dependence of the chemical equilibrium constant for peracetic acid synthesis from acetic acid and hydrogen peroxide in an aqueous solution, derived on the basis of the van't Hoff and Kirchhoff equations, was proposed. The reverse trend of the chemical equilibrium constant vs. temperature was apparent when the predicted values of the constant were compared with experimental ones taken from the literature. However, using the proposed model to calculate the chemical equilibrium constant resulted in better prediction of the equilibrium composition for peracetic acid synthesis at 297.5 K than using experimental data from the literature.